The invention relates to an antenna apparatus for ensuring the quality of communication in mobile communication, and more particularly, to an antenna apparatus in communication systems, in which the CDMA system is used to comprise a direct spread system.
In order to remove multiple reflected waves and interference from other users in mobile communication, there is provided an adaptive array antenna, which uses a plurality of antennas to adaptively control weighting thereof to direct null in a direction of interference signals. For example, FIG. 10 shows an embodiment of an antenna apparatus having an adaptive function disclosed in Japanese Patent Laid-Open No. 162799/1997. The reference numeral 10 denotes transmitter-receivers, 19 an antenna, and 20 adaptive control units.
As shown in FIG. 10, signals received by two elements are distributed and made inputs to the respective transmitter-receivers 10. And the adaptive control unit 20 is arranged for each of the transmitter-receivers 10 (each user) to perform removal of interference. The reason for such arrangement is that algorithm used in mobile communication is usually based on the minimum mean square error method, in which reference signals resembling (highly correlative) desired signals are used. The evaluation function Q of the minimum mean square error method is represented by the following formula.
Q=E||r(x)xe2x88x92y(t)|2|xe2x80x83xe2x80x83(1)
E[xe2x80xa2]: expectation value
r(t), y(t): reference signals and array outputs
As described above, conventional constitutions cause a problem that an adaptive control unit is necessary for each of transmitter-receivers to increase the number of channels as well as scale of an associated apparatus. In CDMA systems, since it is necessary to perform adaptive processing after despreading, the problem with respect to scale of an associated apparatus is made significant with an increase in the number of channels. Also, in the case where the adaptive function is to be added to existing apparatuses, there is the need of designing the entire transmitter-receivers in consideration of adaptive control and replacing all elements by new ones. Therefore, other devices are much influenced thereby, and there are caused problems in terms of various aspects such power consumption, installation cost, installation quality and the like.
The invention has been contemplated to solve the above-mentioned problems, and has its object to realize an antenna apparatus in mobile communication, which is simple in construction to remove interference signals responsible for deterioration of the quality of communication on other users.
An adaptive array antenna apparatus according to the invention comprises a main antenna, an auxiliary antenna smaller than the main antenna, an adaptive control device having weighting means for applying weighting to signals output from the main antenna and the auxiliary antenna with the use of a predetermined weight coefficient, and synthesizing means for synthesizing signals, which are output from the main antenna and the auxiliary antenna and to which weighting is applied by the weighting means, and a weighting control device for calculating a weight coefficient so that electric power of signals output from the synthesizing means becomes minimum, and for outputting the calculated weight coefficient to the weighting means to control weighting, the adaptive control device acting to output signals output from the synthesizing means, to transmitter-receivers.
An adaptive array antenna apparatus according to the invention comprises a distribution synthesizer connected to a main antenna provided in a base station for distributing and outputting signals received by the main antenna, an auxiliary antenna, of which size is determined depending upon levels of interference signals of an environment where the base station is installed, and an adaptive control device having weighting means for using a predetermined weight coefficient to apply weighting to signals output from the main antenna and the auxiliary antenna, synthesizing means for synthesizing signals, which are output from the main antenna and tile auxiliary antenna and to which weighting is applied by the weighting means, and a weighting control device for calculating a weight coefficient so that electric power of signals output from the synthesizing means becomes minimum and for outputting the calculated weight coefficient to the weighting means to control weighting, the adaptive control device acting to output signals output from the synthesizing means, to transmitter-receivers.